The present invention relates to metal panels having a system of internal tubular passageways disposed between spaced apart portions of the thickness of the panel. Said panels possess utility in heat exchange applications wherein a heat exchange medium is circulated through said passageways. A particular application of said panels resides in devices utilizing solar energy, and specifically, solar energy absorbing devices for elevating fluid temperature.
It is well known that the radiation of the sun can be collected as a source of energy for heating or cooling or for direct conversion to electricity. Heating and cooling depend upon collection of rays of solar energy in a fluid heating transfer system. The heated fluid is pumped or allowed to flow to a place of utilization for the thermal energy it has acquired.
In certain areas of the world, solar energy is the most abundant form of available energy if it could be harnessed economically. Even in more developed areas of the world, the economic harnessing of solar energy would provide an attractive alternative to the use of fossil fuels for energy generation.
One of the problems attending the development of an efficient system for the conversion of solar energy resides with the structure and design of the solar energy absorbing device, or solar collector. This solar collector generally comprises a rectangular plate-like structure possessing channels or passageways for the circulation of the energy absorbing fluid medium. Conventionally, these panels have comprised a pair of opposed expanded passageways, known as headers, which are placed at opposite ends of the panel, and are connected by a plurality of tubular passageways which are often in parallel relation with respect to each other. These passageways, as well as the headers themselves, have generally been disposed at right angles with respect to each other and in parallel relation with respect to the horizontal and vertical dimensions, respectively, of the panel.
The aforementioned configuration suffers from certain deficiencies in that the parallel relation in which the connecting portions are often placed appears to render the heat exchanger susceptible to bending or warpage under stress in the instance where the heat exchanger comprises a flat panel. This bending often occurs in both the longitudinal and transverse axes and can, in certain instances, result in blockage of one or more of the tubular passageways by a crimping effect occurring when the panel bends.
A further difficulty has been observed in the instance where heat exchangers of the type described above are employed in systems which undergo exposure to extreme temperature changes wherein the heat exchange fluid is exposed to temperatures which could cause freezing thereof. In this particular instance the units employing substantially parallel connecting portions were found to rupture during tests where fluid was placed therein and frozen, and then allowed to thaw. This type of testing is critical, as resistance to freeze-up is necessary in the event that a heat exchange system fails and fluid remains in the connecting portions.